Development of an Anti-washout Underwater Concrete for an Undersea Concrete Structure Repair

Samita Chaikasatsin; Chalermchai  Wanichlamlert; Parnthep  Julnipitawong; Somnuk  Tangtermsirikul

Samita Chaikasatsin School of Civil Engineering and Technology, Sirindhorn International Institute of Technology (SIIT), Thammasat University
Chalermchai Wanichlamlert Construction and Maintenance Technology Research Center (CONTEC), School of Civil Engineering and Technology, Sirindhorn International Institute of Technology (SIIT), Thammasat University
Parnthep Julnipitawong Construction and Maintenance Technology Research Center (CONTEC), School of Civil Engineering and Technology, Sirindhorn International Institute of Technology (SIIT), Thammasat University
Somnuk Tangtermsirikul School of Civil Engineering and Technology, Sirindhorn International Institute of Technology (SIIT), Thammasat University

Keywords: Underwater concrete, Self-compacting concrete, Viscosity modifying agent (VMA), Anti-washout

Abstract

This paper aims to develop an anti-washout underwater concrete (here-in-after called underwater concrete) that can be cast in water without washout of powder particles by water. The underwater concrete was developed following self-compacting concrete (SCC) method. For preliminary study, the underwater concrete was investigated from the anti-washout ability of cement-only mortars and cement mortars with fly ash by visual method with sand to mortar ratios (S/M) of 0.3 to 0.35, water to binder ratios (w/b) of 0.3 to 0.4. For viscosity modifying agent (VMA), this study used 2 components of extra high-performance thickeners (VMA) which were Mighty VT100A&B as VMA component 1 and Mighty VT200 as VMA component 2 with dosages of 4 to 9% and 2 to 5%, respectively and a superplasticizer (PC based) with the dosages of 1.5 to 2%. The mortars achieving anti-washout ability were used to design concrete mixes with the same sand to mortar ratios (S/M) and water to binder ratios (w/b) but the amounts of both VMAs and superplasticizer (SP) were increased (Mighty VT100A&B with a dosage of 10 %, VT200 with a dosage of 7 % and SP with dosages of 2 to 2.5 %) in order to achieve anti-washout ability and workability (slump flow of 650 to 750 mm, V-funnel time of 60 to 80 sec) and to achieve static segregation resistance before setting time (22 - 24 hrs.) and L-box tested with water filled in the box (passing ability under water). This underwater concrete was developed for a repair project of the port authority of Thailand at Samut Prakan province where marine environment conditions such as chloride resistance, sulfate resistance and non-shrink ability must be considered, and these were achieved by applying 10 % of fly ash and 30 kg/m³ of expansive agent in the concrete. As mixing process of the concrete caused entrapped air of about 8-12 %, a de-air admixture was used to reduce the entrapped air to prevent viscosity loss and settlement of the concrete due to the high content of entrapped air.